There is substantial disagreement among clinicians concerning the etiological significance of impaired nasal respiration. conflicting views remain in spite of many attempts to estalbish a causal relationship between dento-facial deformities and nasal airway impairment. The controversy stems from a lack of reliable, quantitative techniques to assess mouth breathing and nasal airway adequacy. Indeed, an accepted, quantitative definition of nasal airway impairment in physiological, as well as clinical terms, is unavailable. We have developed a new technique for simultaneously recording oral and nasal respiration which for the first time will allow the characterization of respiratory mode (moth and/or nose breathing). The data which we generate should provide the information necessary to assess the upper airway, define impairment and determine respiratory mode. Our investigations will include: (i) analog model studies of simulated respiration, and (ii) clinical/physiologic studies of the inspiratory and expiratory characteristics of the upper airway. The model studies will provide information on the effects of airway size and shape on the aerodynamics of simulated breathing. The clinical studies will attempt to relate oral facial morphology (facial proportions), cranial posture, and respiratory mode to physiological parameters associated with breathing. The results should enable clinicians to (i) objectively quantify and characterize breathing mode, (ii) distinguish between normal and impaired naso-respiratory functon, and (iii) measure quantitatively the effects of treatment aimed at improving nasal respiration. This should provide a better method of assessment of the upper airway, assist in the identification of children whose oral-facial development may be compromised by respiratory problems, and possibly reduce the frequency of unnecessary surgery.